Probably massively overthinking this but...
Yesterday my ds 2yowas fine, ate all his lunch and was playing with his sister ect. Then we all went outside to play football and have a run around. Dh kicked the ball trying to get it in the goal (kicked it hard) and as it was about to land ds ran in front of it before I could stop him and it hit him on the front of the head. He wanted a cuddle but didn't really cry. Then when we came back home and gave him dinner he didn't eat any of it (not like him at all). Seemed fine at bath time and went to bed like normal.
Then this morning he's started projectile vomiting, no temperature, very pale skin and he just wants to lie on me on the sofa. Could it be related or is it likely just a bug and coincidental timing?